Fluid ejection devices in inkjet printers provide drop-on-demand ejection of fluid drops. In general, inkjet printers print images by ejecting ink drops through a plurality of nozzles onto a print medium, such as a sheet of paper. The nozzles are typically arranged in one or more arrays, such that properly sequenced ejection of ink drops from the nozzles causes characters or other images to be printed on the print medium as the printhead and the print medium move relative to each other. In a specific example, a thermal inkjet printhead ejects drops from a nozzle by passing electrical current through a heating element to generate heat and vaporize a small portion of the fluid within a firing chamber. In another example, a piezoelectric inkjet printhead uses a piezoelectric material actuator to generate pressure pulses that force ink drops out of a nozzle.
Although inkjet printers provide high print quality at reasonable cost, continued improvement relies on overcoming various challenges that remain in their development. For example, during periods of storage or non-use, the nozzles in inkjet printheads can develop crust and/or viscous ink plugs in the bore area. Viscous plugs or solid film-like crust in the nozzle bore area can form as a result of ink drying and ink component consolidation. The plug or crust prevents a drop from firing when the nozzle ejection element is actuated. Other challenges that continue to adversely impact print quality and cost in inkjet printers include air bubble management and pigment-ink vehicle separation (PIVS) in printheads, which can cause ink flow blockage, ink leaks due to drooling, partly full print cartridges to appear to be empty, and general print quality degradation.